Abstract

Podocyte malfunction occurs in autoimmune and nonautoimmune kidney disease. Calcium signaling is essential for podocyte injury, but the role of Ca2+/calmodulin–dependent kinase (CaMK) signaling in podocytes has not been fully explored. We report that podocytes from patients with lupus nephritis and focal segmental glomerulosclerosis and lupus-prone and lipopolysaccharide- or adriamycin-treated mice display increased expression of CaMK IV (CaMK4), but not CaMK2. Mechanistically, CaMK4 modulated podocyte motility by altering the expression of the GTPases Rac1 and RhoA and suppressed the expression of nephrin, synaptopodin, and actin fibers in podocytes. In addition, it phosphorylated the scaffold protein 14-3-3β, which resulted in the release and degradation of synaptopodin. Targeted delivery of a CaMK4 inhibitor to podocytes preserved their ultrastructure, averted immune complex deposition and crescent formation, and suppressed proteinuria in lupus-prone mice and proteinuria in mice exposed to lipopolysaccharide-induced podocyte injury by preserving nephrin/synaptopodin expression. In animals exposed to adriamycin, podocyte-specific delivery of a CaMK4 inhibitor prevented and reversed podocyte injury and renal disease. We conclude that CaMK4 is pivotal in immune and nonimmune podocyte injury and that its targeted cell-specific inhibition preserves podocyte structure and function and should have therapeutic value in lupus nephritis and podocytopathies, including focal segmental glomerulosclerosis.

Figure 1

(A) Representative images of immunofluorescence for nephrin or CaMK4 from patients with LN (n = 10) or FSGS (n = 10) or from a subject without renal disease. Green or red color represents nephrin or CaMK4, respectively, and merged figure shows the signals from nephrin, CaMK4, and DAPI staining. Scale bar: 50 μm. (B) Representative images of immunofluorescence for nephrin or CaMK2 from patients with LN (n = 10) or FSGS (n = 10) or from a subject without renal disease. Green or red color represents nephrin or CaMK2, respectively, and the merged figure shows the signals from nephrin, CaMK2, and DAPI staining. Scale bar: 50 μm. (C and D) Time course of CaMK4 expression in human podocytes after exposure to IgG from LN patients (L) or healthy donors (N) (C) or LPS (D). The data are representative of 3 independent experiments. (E and F) Time course of CaMK2 (arrow) expression in human podocytes after exposure to IgG from LN patients or healthy donors (E) or LPS (F). The data are representative of 3 independent experiments.